Can't get my license plate light to work. Need help.

[j-dogg]

I bought new bulbs and that didn't work. I checked the bulbs on another truck and they all worked fine. I bought a brand new license plate light assembly thinking the old one was too rusty and that didn't work. I cleaned the old assembly thoroughly and that didn't work. The weird thing is that I am getting power all the way to the point of contact for the bulb, but it just won't come on. Is there some sort of ground I don't know about. This is really irritating because I can't drive at night until it's fixed.